There has been recently released on the commercial market by the Eastman-Kodak Company a new form of 35 mm film cartridge (Trademark "DX") provided with means whereby the speed of the film within is indicated on the outer surface of the cassette by a five-digit coded pattern of dark insulating and bright conductive areas thereon. The insulating areas area coated on a common conducting area on the cartridge so that the exposed conductive areas become code sensing areas. There are thus five possible conductive sensing areas employed to yield a representation of the film speed, represented by the arrangement of insulating areas.
The purpose of this film coding system is to allow control of camera exposure for a given ambient lighting condition as detected by photosensor means in the camera so as to set the correct value of aperture, shutter speed, or both according to the film speed as indicated by the pattern of insulating markings on the cartridge. The applicant is aware that experimental systems have been demonstrated wherein electrical contact to the speed-defining pattern is made by electrical probes making pressure contact to these speed-indicating sensing areas, these probe sensings in turn being communicated to a microprocessor unit using a table-look-up program to establish an exposure control signal according to the precise filmspeed value. It would be a useful feature in a camera if the same function could be provided from such sensings without requiring a microprocessor so as to reduce the cost of the camera.